No Power to the AC compressor

[ajcook5]

Hey everybody, I'm looking for some help getting my ac up and running.

Details: 2000 mkIV jetta tdi, no power to the ac compressor

What has gone on so far:
Started with a simple resistance test on the compressor and it had infinite resistance. At the time I didn't test for power to the compressor. Ended up replacing the compressor, receiver drier, and condenser (cracked line while removing the drier). After getting the new parts installed I evacuated the system with a vacuum pump and started to refill the system but since the compressor didn't kick in I only have the system about half capacity.

Checked fuses 5, 16, 25, s164, and s180. All good.

Since that point I have tested for power at the compressor and have none (new compressor is good btw). Then I tested the High pressure sensor, ambient air temp sensor, and started to test the fan control module. I am really looking for help with testing the FCM. Specs and procedures that go with that. The fans did run when I got some fluid back in the system but I could tell a difference between slow speed and high speed.

Thanks for reading and any help provided!

 

[Herm TDI]

Are both A/C fans running ?

 

[ajcook5]

Are both A/C fans running ?

yes both fans are running

 

[JETaah]

I am by no means an A/C expert but I know that that A/C wont kick on if there is not enough static refrigerant pressure in the system or if the pressure is too high.

A common issue on the A4 cars is broken wires right at the 4 wire connector on top of the starter wiring bracket. Two wires go to the alternator charging signal/idiot light and two go to the A/C clutch coil.

So, if the fans are running but the compressor coil is not engaging, I might suspect the wires at the 4 wire connector or an open circuit in the clutch's coil which can be checked by hooking 12v right to the connector on the compressor.

 

[Genesis]

He said he already checked the coil, and since the fans run on low with the button in and the ignition on after he started putting gas in (the low cut-out is ~35psi, roughly, on the high side) the system "sees" the fact that there's a charge in it.

That 4-pin connector looks like a good place to check next since the compressor clutch coil is now known good.

 

[JETaah]

Here is a troubleshooting guide to the system in your car. It is a lengthy thread but a bunch of relevant info is in the first post.

If I am not mistaken, in one of the links in the first post, there is a pin-out and "what readings to expect" when you check them, for the fan module.

http://forums.tdiclub.com/showthread.php?t=242699

 

[ajcook5]

Thank you everyone, just got back in town after a short vacation. I will do some checking tomorrow and see what I can find!

 

[Tdijarhead]

This is where I found my problem. That four wire connector is located on top of the starter. There are actually numbers 1-4 on the connector itself. Numbers 3 & 4 go directly to the ac compressor.

 

[ajcook5]

Found two broken wires, one at the connector above the starter and one hidden under the battery. Fixed the wires, AC works! Thanks guys!

 

[Genesis]

Excellent!

 

[bassmachine]

Thank you! although I still never figured out how to unlock the purple secondary barrier on that D-connector, looks different compared to all other tutorials out there

 

[[486]]

Thank you! although I still never figured out how to unlock the purple secondary barrier on that D-connector, looks different compared to all other tutorials out there

just butt connector the wires beside the connector
that one actually doesn't really even need to come apart even when you're stripping the harness out of a parts car, much less any sort of service like removing the engine for repair (where you'd just be flopping the whole harness aside)

 

[Sayyess]

Had the same issue but figured out it was just a valve that was out of place. Check that again! I've rarely seen compressor issues in the car shop I work for and we have a lot of cars coming in on a daily basis. What I notice a lot is people coming in with flat tires, or tires that are not inflated correctly and can be a dangerous trip that can lead to disasters. It's actually funny since there are so many cheap air compressor you can buy in the market and have it for other users too. For example a Craftsman air compressor will cost you less than $200 and he's one of the best in the market.

 

[Stupendous60]

Great info! On one of mine, when checked initially, I verified the fans, and memory tells me ac was cooling..Then later no cooling, fans working, wha happin? I realized, after reading this post, the starter was replaced shortly after initial assessment. Voltage check with test light shows no voltage, DVOM across clutch coil shows 9.0v, substituted fan control module, no change. Time revisit top of starter, Thanks to all who have gone before me!

 

[Bloodsweatandmoney]

I had a constant 9v to the plug in the ac compressor. Changed the fan control module with two different ones I got from the junk yard still no ac and only 9volts. Anyways the fan plug to the FCM. The two smaller wires in that plug one is a constant hot and the other only gets 12v when the ac switch comes on and you have enough pressure in system to activate it. I spliced in a wire and connected it to the green wire on the ac clutch. BOOM I have ac again. I know some of you won't like doing this but I have $75 in this car now. So idc

 

[contreeg]

I had a constant 9v to the plug in the ac compressor. Changed the fan control module with two different ones I got from the junk yard still no ac and only 9volts. Anyways the fan plug to the FCM. The two smaller wires in that plug one is a constant hot and the other only gets 12v when the ac switch comes on and you have enough pressure in system to activate it. I spliced in a wire and connected it to the green wire on the ac clutch. BOOM I have ac again. I know some of you won't like doing this but I have $75 in this car now. So idc

Hello I'm having the same issue with my ac wiring under the battery. After months of splicing wires at the harness on top of the starter and having ac shut off with vibration from running engine and freeway speeds, I want to just start over and add new wire from FCM to clutch. Do you have a picture of the smaller wire you spliced from? Pin or labeling maybe at the FCM harness?

Thanks and great job